The treatment of sites involving surgical difficulties or minimally invasive therapy to the human body is often accomplished with a balloon catheter, which is provided at its distal end with a balloon capable of expansion and contraction.
On type of balloon catheter is a vasodilative balloon catheter, which is applied to PTCA (Percutaneous Transluminal Coronary Angioplasty) to expand the narrowed area in a blood vessel such as coronary artery. PTCA consists of securing the femoral artery by the Seldinger Technique, inserting a guiding catheter to the proximity of the lesion (or the narrowed area of the blood vessel), with a guide wire preceding, passing a balloon catheter through the lumen of the guiding catheter, placing the distally located balloon of the catheter at the narrowed area, and injecting a fluid to the balloon through the lumen formed in the catheter body, thereby expanding the balloon so that the narrowed area is expanded.
Expansion of the narrowed area in the blood vessel is also accomplished by placing a stent in the blood vessel. Stents generally fall into two categories—the self-expandable type made of elastic material, and the balloon expandable type which remains contracted before use and is expanded after placement. The stent of the second type is delivered to the narrowed area in the blood vessel by a balloon catheter used for stent delivery, is then expanded as the balloon is expanded and is finally implanted at the lesion.
Another category of balloon catheters includes balloon catheters for IABP (Intraaortic Balloon Pumping) which assist the heart to pulsate by the balloon's periodic expansion and contraction in the aorta.
Balloon catheters mentioned above are required to have good trackability which permits a balloon catheter to advance smoothly to the desired site through a sharply meandering catheter or blood vessel. These balloon catheters should have a balloon that meets the following requirements.    1. The balloon should have sufficient strength and impact resistance to withstand the rapid pressure change or increase that occurs at the time of expansion. Also, the balloon should be strong enough not to break on contact with calcified hard living tissues.    2. The balloon should have adequate flexibility for trackability.    3. The balloon should have adequate compliance such that it is flexible but does not expand further once it has expanded to the desired diameter.    4. The balloon should have a self-lubricating surface so that it advances smoothly through the sharply curving or meandering catheter.    5. The balloon should have good dimensional stability to ensure that the balloon retains a uniform diameter and film thickness after expansion.
Balloons in the past, however, do not satisfy these requirements. Those made of polyamide or polyethylene possess good flexibility but lack strength, impact resistance, non-extensibility, self-lubricating property, and dimensional stability. Those made of polyethylene terephthalate have non-extensibility but are poor in strength, impact resistance, self-lubricating property, and dimensional stability.
There has recently appeared a balloon having a layer of oriented polytetrafluoroethylene which is disclosed in JP-A-2005-520639 (hereinafter referred to as Patent Document 1). It has non-extensibility and self-lubricating property but lacks impact resistance and dimensional stability. Another disadvantage of this balloon is that polytetrafluoroethylene has to be molded at a high temperature on account of its high melting point and hence needs an expensive molding machine that is able to withstand high temperatures.
For these balloons to have improved strength and impact resistance, they need sufficient film thickness. A balloon of a thick film adds to the outside diameter of the catheter when it is folded and wound around the catheter. The increased diameter prevents the catheter from being inserted smoothly into the guiding catheter or blood vessel.